Influence of Si Supplementation on Growth and Some Physiological and Biochemical Parameters in Salt-Stressed Tobacco (Nicotiana rustica L.) Plants

Tobacco is a salt-sensitive glycophyte crop species. In this work effect of silicone (Si) supplementation (1 mM as Na2SiO3) was studied in Nicotiana rustica L. cv. Basmas grown hydroponically in growth chamber under control, low (25 mM) and high (75 mM) NaCl concentration for two weeks. Dry matter production of leaves was depressed by salinity level as low as 25 mM and higher salt concentration decreased plants dry weight by 52-82%. Si supplementation alleviated salt stress effect as could be judged by higher dry weight of shoot and roots in +Si plants compared with –Si counterparts. Leaf chlorophyll a and carotenoids concentrations and net assimilation rate were higher in Si-treated plants not only in salt-affected but also in control plants. Si treatment resulted in higher concentration of soluble carbohydrates but not proline. Leaf transpiration rate, unexpectedly, was not diminished by Si and water use efficiency was rather lowered by Si in salt-treated plants. Si application caused a slight reduction of Na concentration while increased that of K and Ca significantly and resulted in higher K:Na ratio in the leaves, stem and roots. Our results suggested that Si application improved tolerance to salt stress in tobacco due to an enhancement of photosynthesis, accumulation of organic osmolytes as well as improvement of K:Na selectivity but not limiting water loss. In addition, greater dry matter production of Si-supplemented plants in the absence of salt was associated with elevated photosynthesis rate, higher K and Ca uptake and proline content.